Telephone system



2 SHEETS SHEET 1 Zia/F2727 I [252-155 5Z7EIT'A'5 Dec. 26, 1922. 1,440,111

0. SPARKS TELEPHONE Svs'reu' FILED MAY 23, 191B 2 SHEETS'SHEET 2 Zia/927702". IZYEPZE'E Sparks.

E57 Y 1L 7- Patented Dec. 26. 1922.

e euremxoeercim museum! 8mm emimmmwenmea. 1m; z1mm J10. :zzuunl i wan I!!! nausea A feature 01; .my m wenuon 1s .to ,arrange the; operabors'mele hone-circuit. in such a manner that theimde tone redueingiheans is always in eircuit endopereting .to reduce the side-bone in the operabers receiver.

.A further object of my invention is the revision of means for eutometicelly renering the o lgorsreceiver inoperative by disassoeietmg itfromlhe nepeeting coll mechanism when the. nherafn'xsl telenhone is not in use.

A further object of my invention is the conneetiou of the ogeratovs' receiver in a. Wheetsjjone bridgecxrcuii; b0 reduce the side tone while the operators telephone is in use for eonversirzw.- with telephone subscribers 'zmd to either aieessociete .phe operators recelverjrom such Wheetstoue bridge circuit \yhenthe operator's, telephone ,is not, used in conversing with subscribers, or to maintein a balance of the Wheatstone bridge circuit while the operators telephone circuit is not in use.

. whe e o a 2900 v A flhewrdveireuib Uior K these? rel-w) .AT. The, unsWeI ingHsIeBVeWuBer juel; J- of e calling me, and'the allSjwiniging 0 the answering supervisory le'm" AL. A;

circuit C. A- leeull relay RE is also rovidof conversation toplace .tlle cord circuit in RE is also we ized, should the calling sub- M M filhPl e-m m i. ay the he'awly mafked .coh'duc e. ii

fidecl with an an ering slhejge-eupenvisdry e5 relay AS. and. an answefmg'1311ieupelr'vi si 1 3g' \fis 01-y.1 ?ln l -S i's adqpted fib be ene whentheflfiswering {hug in hip, guperfllsory relay AT -is "zed fife: the line. The Ewoxel'ays. exid' Teont'rbl" listening relay LS is provided .w loll :is .e'pergizedupoh the imtuetioulof .tlieielaly AS to (xmnect the VOPQIFl-t-OI S set 0 of Yeufihm to the col-cl cbnductprsof the cord ed which is energized wlieii the eallihg subser'lher restores has receiver after-termination 10) condition to allow the mlling subsctiber to recall, should he wish to do so. The relay scriber replace 1is receiver before the called subscriber answers, to disconnect ringing supervisor current from the called line. A combined recall and manual ringing key K is provided, which=ke y ignored tor-the left to seize nect th operators set Q from the conduc- [ill tors. 1K *p'arty" line rin'ging key RK is also provided for connecting one-of a plurdlftyofiringinggeneretors G, G, G, and (i'ltWsigflhPe subscriber at the called-for sulistetion interrupter relay IR is enerup'on the ectuetionot the party line ringing key RKiio close a circuit for the cohtroIfihy'RC; which relay contro'ls th'e connection ofringing current to the called line and also connects the interrupter ms chs-in srruiierrelsym; A calling 5 CT is-zilso provided,"

siiise'rvistr ssn; is adaptedfii'ile" en'e'rgiz'ed'upon theres'ponse, om subscriber-"nth celled subeteti'on to lithe ciicuit'foFthe'ringing control relii" Cto disconnect .tli'e'rin "ng current fishe men-circuit C. A c ing superv 1am; JCLHS nlsoprnvidnrl For the usil e 'urposes,

- 'friieliiihltf'rgeroer in invention compriseyalii'ihdiic tion coil IC nilt up of four windings, 1, 2 3 and, and the usual incu -pan can 1d and retardation coil RA for testing S r ass to produce a' click in the operiito s head trec'eiver 5 when a bu line is 'test3d"as is well known, An artificial reis connected in'circuit with the seco'r'ida," windings 3and 4 of the induction coil 1C, the'said resistance 7 forming one arm of a Whentstone bridge circuit. The windings3 and 4 of the induction coil IC rem two of the other arms of the bridge, and the suhscribers line, including the circuit connecting wires 8 and 9 which extend throii h contacts 10 and 11 of the listening relal' l s 'for'ms the fourth arm of the said br i e circuit. The fourth arm of the Wheatstone bridge of the operators set 0 extends from one terminal of the winding 8 of the induction coil IC over conductor 8, through contact 10 of relay LS, over the subscribers line which is connected to the.

cord circuit C when the answering plug AP is inserted into the jack J, through contact 11 of'relay LS and conductor 9 to point 37, and thence over conductor 36, through contacts l2 and 13 of relay LS and over con ductor 35 to a terminal of the resistance 7. The head receiver 5 of the operators circuit is connected across the circuit, having one terminal connected between the windings G5 which is energized 3 and 4 of the induction coil 1C, and the other terminal of the head receiver is connected; to-normelly open spring contacts 12 and 11 of r'eley'LS. When the may LS is energized, the last said terminal of the operatofls receiven'is-conneoted .to. one side of the calling line and tonne terminal-of resistance coil 7. The circuit of the heed receiver biis normally open to the transmitter side of the operators circuit when the operators circuit ls'not in use, that is, when the operator is not answering cells When the operetors set Die in nsein answering cslls 'the'receiirer 5 and its circuit is connected; due to the closing of contacts 12 end l3 u poiithe actuation of relay BS. The re ceiirer' 5"in this'case bridged across the Wheiitstiine bridge circuit, comprising resistaiii'ce'i, windingst and 4 of the'induction lC and the loop of the subscribers line, to 'rediich'fthq' side tone the said recei'ver ances r s srtwrs-eransiinmr-n as will b z-fe "lieifeihelfter'described.

Scmewhi't sinnsrcwuishm been used to reduce the side tone efiect'in the opeggc r's ec i m but fthes circuits-have. all been'fiinftyfiorithereeson new when th'eope'riitors setis'notin use, one of the arms of the Wheetstone'hrid circuit is'left'open, nnjinljl the arm slashin the suhscribers line, while the otherthree ar'ms includin i itn'fni i sebf' the'ertifie lelfieslstence 7; are left closed, thereby causin' the potential" across the receiver s to, become unbalanced, and any disti'lrbaizce in the vicinity of the oper etorsfitrcnsinitter would be transmitted to thecperi to'rs'r'eceirer, giving a side tone effeet;'j*In"other words, such prior circuits only reduced the side tone during the periods that the'opcrators set was in use. To overcome the fault of such prior circuits, I have opened up the arm ofthe Wheatstone bridge including the artificial resistance '7 so that the o orator is not bothered with a side tone curing the eriod when her set is not in use. Each cor circuit is pro ided with a )ai'r of contacts to close this arm of the entstonc bridge when the arm including the 'subscribers line is closed.

Referring now in general to Fig. 2,1 show a modified form of an operators set or circuit O opersting in connection with another form of telephone system from that illus trated in connection with Fig. 1. In Fig. 2, I show a. calling substation A and e called substation B, the said substations A and B terminating respectively at the exchange in. line circuits L and L. The line circuits L nnd L at the exchange comprise respectively the usual line relay LR and LB", cutoff relays CO end C0, multiple jacks nnd J, and multiple line signals S and S The jacks of the lines are distributed among the difi'erent operntors positions, and there induction coil and is aline signal for each jack at the different operatorspositions so that when a call isinitiated over any line, the line sig nals. at the difiercnt operators positions are lighted and any one of. a pluralit of operators my seise'the eall-to'the cxc nsion of the other operators.

: Thai cord circuit 0 for interconnectin(gl the subwationsA and 58' as calling an called) is provided with an answerin plugnhl and a calling plug CP, the sa: plugs-AB? andCP' be ng connected=by the heavil marked conductors. The answering end 0 .the cord circuit C is provided wit a. sleeve nelay ST-which is energized when an answering. lug AP is inserted into a jack J o'i-a line. The relay ST is providedt-wi a' igh and'low resistance winding, and upon the actuation of relay ST tlmhi'gh. resistance winding isshunted thus 'prevents' the same relay from be energised in i another -cord circuit shoul oordmema'ining atnorma she does not reoeivean answer from, the calling'sub'scriber and withdraws the answeii plu of her linkcircm'tfromtlieconn ac Asupervisory relay SIR-is provided which is actuatedru on the energxzation'of relay ST, the said re ay operating oven the line. The relay SR. upon actuation prevents-the premature lightin of' the answcrin su rvisory lamp A listening re ay S is also provided and is actuated in response to the energization of relay ST to connect the operators set or circuit 0' to the cord conductors. A link disconnect relay LD is rovided which is energized when the c g subscriber replaces his receiver after conversation to open the link conductors to allow the line circuit of the calling subscriber to restore to normal to erznit the subscriber to recall. The relay D also operates when the calling subscrlber replaces his receiver and before the called subscriber answers to disconnect the ringing current from the called line.

The calling end of the cord circuit is provided with a sleeve relay SL actuated when the callin plug CP' is inserted in the jack of a called line.- The sald relay SL upon energizing opens the circuit of the listening relay LS, which relay de-cnersizes to disconnect the operators set 0 from the cord conductors. A party line ringing key RK is provided for connecting and one of a lurality of r' nerators G G, G Ci and G to sgriifi he called-for subscl'i or. A ringing control relay RC is provided which is actuated u n the actuation of the ringing key a The said relay RC upon actuation brings about the energization of interrupter rela IR. The interrupter relay IR is intermi ntly energized and de-energiaed through the agency of the interrupter to connect ringingcur- 78' rent to the called line. A. ringing trip relay HT is provided which is actuated u n the response of the subscriber at the ca ed-fon sulwstation, should the called subscriber remore his receiver in response to the ca'llflO s" nal during a ringing period. The relay it upon its energization interrupts the circuit of the rin ing control relay RC and the said' relay llC in turn disconnects the interrupter l" to allow the interrupter relay to restoreto normal; A supervisor relay SR is also provided which is actuated upon the response of. the calledsubscriber' to interrupt the circuit of the relayRC' should the called-for subscriber answer'dun 9'6 mg a silent period. A- calling s'u erviso'ry lamp CL is rovided and is used for the usual supervisory purposes, as is wen known.

The operators set 0' comprises an in- 96 dnction coil 1C, includin four'win'diii gs,

1, 2,' 3 and 4, and a high resistance retardation coil RA in association with the usual induction coil IQ for testing purposes to produce a click in the operators 100 head receiver 5 when a line is tested and found busy. In the o rators set or circuit 0 shown in Fig. 2, show a resistance 7' for purposes similar to those described in connection with Fig. 1. I also show a resistance 15 equal in resistance to thatof 7 and when theoperators circuit 0 is not in use in establishing connectioms'thisresistence i in association with resistance?" brings about a balance.v reducing the Side tone in the operators head receiver 5', as will be more fully hereinafter described. The resistance 15 is common to an operators position and is serially connected through the listening relays LS of an operators position. In the operators circuit 0, shown in Fig. 2. the zmcretors head receive: 5' is in closed circuit with the transmitter side of the set, and I provide a Wheatstone bridge, the arms of which are the resistance .5. windings 3' and 4.. and the loop includmg conductors l6 and 17 and the resistance 15, the said described bridge forming a balanced circuit for the head receiver 5. When the operators set 0 is connected to the cord conductors clue to the actuation of relay LS,

e'lle resistance 7 and windings 3' and 4 of the coil IC form arms of a V'Vheatstone bridge. and thefourth arm. of the bridge comprises the subscrihers line and theron- 'sistances. -Fig-. 2, instead of opening up-the third arm nesting wires 17 and 18. The Wheat-stone bridge circuit isone balanced for talking currents ratherthan' one balanced in re- In the modified circuit shown in arrangement of the circuits and-apparatus employed in my invention, I will now (lescrlbc it more in detail operating in connection with the exchange systems illusrated Referring now more particularly to Fig. 1, and assuming that the subscriber at the calling substation h initiatcs a call, the re moval ofthe i'eceiventhereat brings about the energization ofsthe. line .relay LR .of the linecircnit L, and the actuation of the said relay- LRr-ibrm about the lightingiof 2% the line signal-.S;-- he operator associated withthe cord-circuit C, noting the lighted line signal S, -,lnserts the answerinfi plug AP of.the cord circuit G into the answering jack J of the calling line. The act of inserting the plug AP into the jack J 010585 c seriesenergizing circuit for the answering sleeve cu ervisory relayAS' of the cord circuit C an :the cut-off relay C of the line circuit L from battery through the winding. of the relay AS, the sleeve contactic of the connected lug AP and jack J, and through the Winding of the relay CO to ground. The answering tip supervisory rela I T is char izecl upon the actuation of-the rela GO om round-through the winding 0 the relay KT, tip contacts of the connected plug AP and jack J, alternate contact 25 of the cut-0E relay CO, through the substation A, back through alternate contact 26 of relay CO, sleeve contacts of the connected plug through the winding of the relay AS to battery and ground. The relay AS energizing prevents the rernctuieliihting of the answerin supervisory lamp A and the energization of the relay CO restores the line relay LE to eiface the line signal S.

The closing of alternate contact 27 of relay AS establishes an energizing circuit for the listening relay LS from battery through the lower winding 28 of said relay, conductor 29, alternate contact 27 of relay AS, conductor 30, and conductor 31 to ground at normal contact 32 of the calling sleeve supervisory relay CS. The closing of alternate contacts 10 and 11 connects the 0perators set 0 to the cord conductors by way of conductors 33 and 34. The closing of normally open contacts 12 and 13 places th head receiver of the operators set in AP and jack J, and

closed circuit with the transmitter side of the .operators set 0 and the resistance .7 is introduced to form a Wheatstonebridge circuit. 5 The four :irms of the said bridg: are included in a circuit which may. traced from alternate contact of relay LS, over conductor 8, through the winding 3 of the induction. coil ID, the winding l of-the-c0il .IG, resistance T, conductor 35, alternate contacts. 12- and 18, conductor- 36 to the point 87,- andgth'encewover conductor 38, through condenser 39,-alltemate contact 11 of relay LS, conductor 34;, and the loop out over -the calling-line and back over conductor 33- toithe alternate contact 10. The head: receiver 5 isconnected in the hridgeht ints 37 and 40'50 that one-half of the bri comprising the winding 3 of the coil IC and the loop above traced forms two arms of the bridge, and the winding 4 ofwthe coil 10 and the resistance 17 form the other two arms of-the bridge. There sistance 7 is such that the .loop as previously described and the said resistance .7 bring about the balance, thus reducing the side tonezcause'd b -the o iatore-transmitterof the-set Oint ereceiveniiz r I The .0 erators' set 0- havin l been' connectecl, no to the closure of a tomato contacts l0 and 11 of listening relay LS, the operator now in uires the wants of the-callin subscriber undassuming thatiit' is the substation B that is wantedytheoperator tests the multiple jack J of the called line by lac g the tip of the callinglug GP to tie cave of thetjhck J, andifthe said-line is busy the o orator will receive the usual busy click in or head receiver 5 in a well known manner; I g

Assuming now that the called line is idle, the opcmtorinserts the calling plug :01 into the jack J of the called line, establishing a. circuit traced from battery through the wind of the rolling sleeve supervisory relay S, conductor '41, sleeve contacts of the connected Slug (JP and jack J and throu h the win ing of the relay CO to groun The relay CS,'upon energizing, o ens its normal contact 32, opening' the circuit of the listening relay LS, which deenergizes and disconnects the operators set 0 from the cord conductors. The 0 ening of contacts 12 end 13 of the relay L again places the head receiver circuit of the operctors seton open circuit with the transmitter side of the set. The closing of alternate contact 32 of relay CS brings aboutv the lighting of the calling supervisory lamp CL over a circuit traced from battery through the said lamp, normal contact 42 of the key K, conductor 43, normal contact 44 of relay RE, conductor 45, normal con tact 46 of the end sprin of ringing key RK, conductor 47, normu contact 48 of the relay RC, conductor 49, normal contact 50 of relay Rn; conductor 51, and normal contech '52 of reMLGTto oundat gilternate contact 32 of t rel 3: The said lamp remains lighted until Uheoprfltor depresses the key BIL- TM: operator now depresses. e-prop'er ringing key plunger to its fullydepressed position to e-lose end firing oontacts io and 57 an? t? comect p p mg "s 'm t- G to si nalthe czaledjsuhscriber at the sub- 4 30 The, closing of alternatecontact 57- of the and: springs. establishes 'fancirguit for tltlfigluteli'lrulfiter releyil tgncgd 1535mm; attar t 5 1 .126! win 5 to the reihy IR (inductor-.59 alternate contact 57 ofthe end springs, con actor 60 ,conductor &9,-norma1 contact 50 of. relejgiR-E, conducton 51 ind nominal contact 52 of relay CT s si at c t ma e c w of e ay (ESQ-{Hi clOsing Q- nlternate contact 61 of e1 y.-.. 9nne m g en n t generator G,-.\yhic ,we. wn assume is the ringing generator selected; thronghnlternate c ntact 53, ore: conductor: 62, through. the alternate =contact.(i 1,to the line, givin on insmnmnqo m first rin .to the called su scriher when the ringing ey is depressed. The closing of alternate-contact $3 of] relnylR closesnnenergizm" circuit or t e ringin cpntIQ] relay. R traced FQm ,hattery h z 'the ind ei h r r' RC, @9 ductor .64',-a,lternate contact 63, conductor 49, normal contact 50, conductor 51- and norm al 'contc-ct 52 to ground at alternate-ebntaotfiQ of relay CS; Thecl of alternate contact 65 of relnyRC establishes a locking cir cuit for the: said relay traced from battery through the winding of the relay RC and through alternate contact 65 conductor t9, contact 50 conductor 51, and contact 52 to 'round at alternate contact 32 of relay CS. he openin of normal contact 48- of relay BG-cfiaces t .e-calling supervisory lump CL. The closing of alternate contact 66 of relay RC connects the constantly rotating interruptcnal in circuit with the interrupter relay IR over a circuit traced from battery through the lower winding 67 of rela, IR, alternate contact 66 of relay RC; con uctor 68, normal contact 69 of the key K, and through the constantly rotating merru'pter IR to ound. The relzg -IR is thus intermittent y energized and e-energized to connect current from the generator G to the calledlinc over a circuit traccdfrom the iuigrounded pole of the said generator G, alternate contact 53 of the ringing key plun er iconductor 62, alternate contact ,61 of relay IR, alternate contact 70 of rela CS tip contacts of the connected pin C and jack J throu h the condenser an call bell of the subscri er at the called substation B, back through the sleeve contacts of the plug 'pervisory relay the relay CS to battery. N normal contact. 52.of..re1ay.QT. 052611811118 CP and geek Jtiggd a.

tact 71 o relay t grow;

The closing of alternate qqg f o m m wonm us can transmits'a. ingusu'bscriber fromthe orator over.

conductor 73*, through reslstence x, lamp-Y, 70

condenser Z, elternatecontact 7 2 of the relay 1B, conductor 74,- alternnte contact '(5 oi-re- Loy RC, the sleeve conductor of the cord' sleevecontacts of; the connectedplug and jack K, thronfih the substation receiver'of 7' the calling su scriber AubflGk-thatfl h ,ti

contacts at the jack) ind pin 1 Agein throu' h the win-1'5 of the ny A'Ito n ,"g v ng hat l g-subscr ber heir ble signal, notifying: hm; "that the exiled 8 subscriber is being gnc eipc lc subscriber. at the substatiomB vis th'us automaticully signalled..until; 1thesnid called subscriber. at, substation BHgmryers in rer.

spouse to the S g l 9 zwnti the lfinme h- 85 scribe! at substation A repla ccshismeoeii er. .Ugon the response ot the callednuhseriheret su station 13, undo onthmdesenei gizntion of r a cumfl xhe calmer t ppsur hook of substation B, b clgthrough slceye through the now closed contacts of the switch 55 contacts of the connecte .lplugrGRandgjock J conductor 41, end)through th win 'ng,of

h Opening locking circuit of 'the relay RC w ich cleenergizes to open itsnlternate contactfifi, disconnectingthe interrupter I firom: relny Relay IR- thus restoresto normal, disconnecting the ringing current from the wanted, line. .Thcsubscribers are now in conversational circuit, the ta-Lkin circuit being traced over theheavily rnar ed conductors.- Should the calling subscriber restore his receiver before the calledi Subscriher answers in response tothe calling signal. the relay AT would:restore, due to the interrupted switchhook contacts at the calling substation A, and due to this de-eneryzization of releyAT an encrgiz ing circuit for the recall relay RE is establisheitraced from battery through the u per winding .77 of relay RE, alternate con act 78 of relay A S, and conductor 79 to ground at normal contact 80 of relay AT. The relay RE upon energizing closes a locking circuit for itself traced from battery throughthe lower winding 77' of the relay 3E its. alternate contactSL conductor 82,-riormal contact 88 of the key K and conductor 84 togrouncl at alternate contact 85 of the-relayC The opening, f normal contact 50 of re- 111 RE opens the locking circuit of the bl she -t m closing relay RC,"fi hich relay restores to=disconnect ringing current-as above described." {l ke of normal; contact '80 brings -e'bout the' l' tingmf 'the-"enswering supervisory relay 'Dover-a circuit traced-"from battery through thelomp A'Lfalteriiate contact 78, and conductor '79 to ground ht normal conte'ct 80. 'lhe callirgg superyisorylamp CL willgalso be Li hte from battery through the said lamp" 'L,' norrne1- cofitact4=2 we fc'a'llingsuperfis'o131n1np traced from balttery through" ornate contact: 42 conductor 86, conductor'fiLnnd norn'm con tact 52, to round at alternate contact 32 g. When' the called subscriber th'circuit oflth'e' c'alling supervisory lamp CL et'contact 52, notifying the operator thait the called subscriber has answered. I After the subscribers have finished conversation, they rephice their receivers upon their respective switchhooks, thereby ltSl' ifig relays CT and AT. Rclav ATJ'esturin? closes an energizing circuit for the recn l'relay RE :is'previoiisly described and the closing of normal contact of relay AT closes a circuit for the nnswering snper- 'visory signal AL traced from battery through thesaid lamp,.alternute contact 78, and conductor 79 to rounri at norm'al contact/B0. Upon the e-energizntion of the r'elay C-In circuit for the calling super lvisory si nal CL is established, traced from battery t rough the lamp CL, normal contact 42 oi the key K, conductor 43, alter note contact 50, conductor 51, andnormal contact 52.0f relay, CT to ground at'altcrnate contact 320i relay CS. The operator noting the two lighted supervisory signals AL and CL, which give an indication to the operator that the subscribers have finished conversation, Withdraws the plugs AP and C? from their respective jacks I and agm i-m ustorin'grehys-AS and CS. The relayAS opens-the circuit of the relay RE, placing them paratus nt. the cord circuit C at normal; e said cordcircuit C is now available fol-establishing other connections. now; that the subscribers have finished conversetion, and before the plu AP-and CP have been withdrewn theca ing subscriber wishw to eal} the removal of the swim 'at"the' 'substation -A' again brings about the energization of the amine!- lng 'tip supervisory relay AT over the line as" 'reviously deseribed,'hnd esreley RE is f 1o ed upyend'due to =t he"-'closur e of alternew contact 87 of said-relay RE the interpter' Ff is in circui with the answering su rvisary 'signel AL over "a lcircm't meet; mm battery through the lamp zen-meme contact 78, 'oo'ndilctqr 79, alter- ,nate contact 80 'ecndiietb'r 88 through alter- "um come-e sty-- ma=ttwg ehe m n interni ten-T 'e'supewisry [caused to flash, delete the 'conn ime itei"f",notifyin the operatbr' 'th'zit the 'suusenbsrnc the su station :A angina ffigrhtdrtglilfltbrbws the M... fw o, in". :v circnil; ofth're'lov fit biitaljt' 83; causing the said relay RE w-wswre and open its contact, 87' tcdiscbnfec'fiTthe-interruptr I -tc efi'ece the'fiashing su r'y signal A'L. The cloeihgbfi hlteth. "-99 of'the ,key K 'brinfs abdilt th'e er l'eigizfition of the *listenihg'l'e ajr LSIdver ,a circuit traced from battery, "through theuppei" winding ,90 of 100 the relaly LS, cph'cliigtor ;9I, alternate eonfact 92, conductor86; conductor 51; and normal contact 52"to 11nd at 'nlte'rnate contact 32. The contacts 10,11; 12' and 1a of the listening relay LS are closed,'connecting 1'05 the o rators s'c't O to the cord conductors.

and t e o rator now inqni'ieq' the wants of the recalling subscriber.

If another suhscrihei', other than B is 'wanted, she removes the calling 'phn: (JP no from the (-nnnecterl jack J end'jnsarts it into another jack of'the: wanted called line. hen'ithe callingplug is'relm'o vegl, the relay CS restores, allowi'ng therelay' LS to de energize; disconnecting e opemtors set 0, 115 and 'another insertion of the' plu GP to nnother jack allows the circuit to e operated as. previously. describei Assumi that it is the callisnbscriber thnt wishes to call, thehv'inkinz of the re 12o ceiver at the ca-llecl'suhstntion B causes the supervisory lump (L to flash, and' the cpcrator in response to the 'fieshing signal CL actuates her key K. as beforejdcscribed closing the circuit of the relay LS from battery '-1 through the lower winding28 of relay Lg, elternnte contact 27 of relay AS, conductor 30, alternate contact 93 of key K, conductor 94 and conductor 79 to ound at normal contact 80 of relay AT. elay LS energizes I as the winding set in flue cord to converse with is now recalling, apparatus in re tor the subscriber further descripio connect the 'ope'l'at'olrn conductors, allowing her the called subscriber who ind-the operation of the establishing-1 connection readily apparent-without tlon.

Referrin now to Fig. 2, I show a, modified form'o op'er'ators circuit 0, operating in connection with a telephone exclmnqe system C. Assumingnoxv that the subsenibernt-tha substation-A initiates a cell, the remomlof the receiver at the substation brin about-the energization of the I5 line-relay R3 'and'the Chain of its altercare-contact ltghts'theline am S- at a plnmlity'of operators positions. Assuniin fiiafiit IS "cdia circuit C thatnnm'vers the call, the insertion of the linswering'i lug AP into -ihe"lck"5 of (lief-calling me establishes "'9. series one "Zing circuit for'the'cnt-ofi 'r nyco o "the line circuit L and the sleeve 'ieliiy ST, the circuit'fur said relays '25 being tra'ctl firoin'hnttery through the windifng's of; ficherelay ST, dr'm'duutor 102,;closerl contact 'l'03 "of Klisconneet relay LD, the 'skeve contebtam the connected JIugAP and f3" and through the winding of so'thecut-oif'relay CO to ground. The closlire-pf lrltemnte contact 104 of relay ST 'filqoesi lowei-resistance circuit thro'u h the low i'eis'tatncc'winding' 105 of relay the circuit traced frombattery through 105 of relay ST, its a'lternate contact 194, over the previously traced Path "to-grdiind'at cut-off relay CO. The iigh resistance winding 106 of relay ST is; shunted; this arrangement providing for-secret 40"rtioe;'as relay ST'of a. second pair of cords'will' not operate in series with the re lav (-Q as the shunt of the low winding of the relay ST "of the col-r1 circuit 1" mnlers the relav Sl of; the second cord inoperative. The closing of alternate mntac't 107 'of relay 8'! establishes nil encrgizing circuit from the :mperviscry relay SR- tl-aced frmn battery through t-llclower winding of the relay SR, conductor 108,

60 normal contact 1 19 of .relay LI), ring contacts of the connected plug: AP and jack J, through the now closed contacts of: the substation switchhcok. back through the tip contacts of the jack J and pine 511". mm

tart 1100f relay LD. conductor Lil through alternate contact 107 of relay S'l. conziuctcr U2 and through the upper wimling of the relay SR to ground.

Thenpening of marginal contact 113 of re- 1:13 SR upon its enm'gizution prevents the premature lighting of the answering supervisory relay AL. The energizction of the relay C0 of the line circuit L opens the 'e'ne'r'gizin circuit of the line relay LR. which re ay restores to eflace the line sign'als S. The closing of nltemate contact 114 of relay ST establishes ,an energizing cinsuit for the listeningreluy LS', the circuit being traced from battery through the wind-mg of the rein-y LS, conductor 115, throng alternate contact 11- and-conductor 116 to ground at normal contact-I17 of the sleeve relay SL. The relay LS n'pon energizing closes its alternate contacts 19 and 20 to connect the o )eretors set 0" to the cord conductors. ou'ld. another operator attempt. to'seize the call after theonerator associated with the cord cimnit "(ysxsconnecterl thereto, the low insistence pcth .throngh'u-ind' of-the rlav' ST -p'revents the'relav T "of the second card from v g operating, ind thelistenin'g relay US ofthe 'theoperator fl0$l8l58l with the.

second cord-fniling to operate does not connect its associatecf operatofs set 0' across the cord conductors, fT-he second :cperatm *swerssthatth sea hasrbeenauswered by another operator will withdrawn the of her card circuit: fro'mi'the 'multiple nae:

m'itter sideof the oberators .1316" side tone of :the operators 14' is'reduced by "means of a. resistance 15.1""The 11% =8istance15 is so ioozinected through closed contacts 201m 20' nf=the'listen" relays of .the oord Eassocicted the op'erators osition. "In; the -c'lmw.ing,'I show relnysLS andaLS Tfor the purpose of illustretionfthe relay 13S "representing the listening relay in thelnst cdrd-ofi-uzr operntorsrgosition-with which the set 0' is aseociate ."'When the oberators not iswlisconnected from theoord conductors of a cord circuit, c W'heatstbne bridge circuit is established which may be traced from 0km- -tirct 20 of relay Lh' ovel' conductor 16. through the sei'inllycloseclrontnctc 20 and 20: of the other listening-relays as" LS and LS. the resistance 15. conductor 95, bonductor 1.8, Winding 3' of the coil IO, winding- 4' of the coil IIC, resistance 7", conductor 96, condenser 97,-and the conrluctor 17v to -the contact 20. The windings 3' and 4" and the resistance I5 and 7 form the arms' of the bridge. and the head receiver 5' of the operators set is connected across the points 98 and 99. thus forming a balancing circuit. reducing the side tone in the head receiver 5'.

When the operators set 0' is in use, that is, when it is connected to the cord conductors of a, cord circuit, the normally closed contacts 20 and 20' are ogened, disconnecting the resistance 15, an a substitute bridge circuit is established from the tip side of the cord conductor 100, thro l1 alternate contact 19, conductor 18, wi igings 3' and 4 of the coil IC, resistance 7', conductor 96 condenser 97, conductor 17, alternate contact 20, conductor 101, through the connected subscribers substation and back through conductor 100 to contact 19. As before stated, these bridges are balanced as to talking currents and not as to resistances. The arms of the bri e comprise the windings 3' and 1 of the coi IC, the resistance T and the loop including the subscrilr ers line. The receiver 5" is connected across the points 98 and 99 in this bridge, thus forming a balancing circuit and reducing the side tone of the transmitter 14' in the receiver 5'. The relay LS upon enegzin closes its alternate contacts 19 and d an opens its normal contact 20', thus connecting the o rator to the cord conductors as just described. The operator now inquires the wants of the calli. subscriber and assuming that it is the su 'criber at the s'ulr station B that is wanted, the o orator tests the multiple jacks J of the clfiled line by placing the tip of the plug GP against the sleeve of the jack J, and if the line is busy, the sleeve will be at a battery potential, causing a. How of battery through the ti of the plug CP. through normal contact 118 of relay normal contact 119 of relay RC, over conductor 100, alternate contact 19 of relay LS, conductor 18, through thewindjn 120 of induction coil IO, and through t o winding 121 of the retardation coil BA to und. This induces an impulse in the wmding 122 of the induction coil IC' to produce -a click in the operators receiver '5, notifying the operator of the busy condition of the line.

Assuming that the line is idle tvhflzOPBl" abor inserts the calling plu C1 into the multiple jack J of the cello line B, closing; a series energizing circuit for the sleeve relay: SL' of the cord circuit C and the cut-nil relay C0" of the line' circuit L", the circuit being traced from battery through the winding of the relay 3L, over conductor I23, through sleeve contacts of the connected plug GP and jack J. and through the winding of the relay CO to "round. The nomnal contact 11'? usumes its alternate position upon the energizution of the said relay SL. disconnecting the ground from the winding of the listening relay LS, which causes the relay LS to release and I disconnect the operators set 0' from the 0rd condu-rtms. The closing of alternate (01111869 124 of relay SL establishes a circuit for the calling supervisory lump CL, traced from battery through the said lamp, normal contact 125 of relay RC. conductor 126, conductor 127. normal contact 128 of relay LD. conductor .129, normally closed contact 130 of relay RT, normal contact 131 of relay SR, conductor 132, and conductor 133 to ground at alternate contact 124 of relay SL The operator non depremes the proper-ringing key cpl r to its fully depressed position to use and 9 ring contacts 138 and 139, and to connect t e r0 r rm generatorto e1 the mil ed-l subset! r at the substation B-.

The closing of alternate contact 139 of the end of the ringing key BK e8- t-ablishes an energiz' ing control relay RC traced from battery through the winding of the said relay conductor 140, alternate contact 139, condoctor 127, normal contact 128 of relay LD, conductor 129, normally closed contact 130, normal contact 131 of relay SR, conductors 132 and 133, to und atnlternatecontact 124 of relay S The relay H3" is also energized during the interval that the key is held down over a circuit traced irom batte through the lowerrwinding 141 of the re y IR, conductor 142, andtbrough alternate contact-138 .of and springs to ound at alternate. contact .143 of relay 0'. Theclosing of alternate contact 118 of relay. IR" connects iringm current from circuit for the ring through the winding of the, relay RG its 0 ening of normal: contact 125 of the relay C brings about the eflacement of the calling supervisory mgnalCL'. The closi v of alternate contact 145 of the relay R- connects the constantly rota-tin interrupter I to the interrupter relay' R, the circuit being traced from battery throu h the upper winding 146 of the relay conductor 147, through alternate contact 145 of relay RC, and through the constantly rotating interrupter I to ground. The relay IR is thus intermittently energized and de-energized to connect rin current from the generator G to the c e line over a circuit traced from the ungrounded pole of the generator G, through alternate contact 134 of the ringing plunger, through the winding 118 of the ringing trip relay RT, conductor 149, alternate contact 118 of relay IR. tip contacts of the plu CP' and jack J through the condenser an cull bell at the called subscribers substa' tion B. and back through the ring contacts of the jack J and plug GP to battery and ground at alternate contact 150 of relay IR. The closing of alternate contact 151 of relay IR transmits ringing tone to the calling subscriber at substation A from the generator G over conductor 152, through arem 1 alternate contact 119 of relay RC,

mntactllflof reluy'llD, tip corifaots'of plug-NP amlja'ck'J; through the snh'stg tion i'ez'eii'er, haclr through 'the Ting contaots of jack J and "plug AP; back throu h-normal contartlflS, and through the lowerwi'nditi of SR to battery nncl' 'uifi-wgi'vmg the-chl ing' 'sulicriber at r xign'ul zmti fji-ng him that the cllpclfillb scrlber'iwheing signaled. The called-sub? sc'zikeiot the-substation "B 'is"-tllus-'auto- "matically si' u'allefl until the cilld' subr ecriliefi ot'su otio'n' BanswerSini-espons'e to his call-sign'hl or until "tlimlliil ribrfleplflngs hisweceivor.

Should the; ushscriber' lit the railed 'su'h- -"statlou='B"' answei-"durin "afsilianfi' iei' io that is, when the relay IE gized condition, of circuit "is thi buih the sup'elfisorv may SR; which? may "'9 tweed nem bmm throughthe lower finding of the Tolay SR","-condii't0r*16; nor'r'ntel contoctllio ofu elef I-R,"ri con-J tacts of the plug GP and incl: J", 1'0 11 the now cloood" cbnt'aote fthcsuhstati'n switchhook; book *through the tip 'oontaclfi' of the jack J and lug-CB, norninl'mn tact 1-18-05 relay IR dbll'dllbibl"15i$lt6lnateoontact 1560f 'rel'ayfSL, and t rough the u per \vinding'of the relay R" to groung. The opening 'of normal contact 131 (if-relay SR opens'the lookingicircuit fort-lie relay RE, which relay de energizes to open its alternate comfort 1&5 opening of the said contact 145 d the interrupter I fromthe upper winding 146 of the relay IR. The said relay IR now remains normal, thus proventingring- Eng current from being applied to the ailed suhscrihers line.

Should the calling subscriber answer during a ringing interval, the ringing current is interrupted, due tothe actuation of the ring.- ing trip relay RT, over a circuit traced from the un 'rouucled pole of the generator G, throng alternate contact 184, upper winding 148 of relay RT, conductor 149, alternate contact 118, tip contacts of the plug CP' and' jack J, through the now closed contacts of the substn tion swil'ohhook. and back through the ringing contacts of the plugCP' and jack J to battery and ground of. alternate contact 150. The disconnection of the condonser at the substation permits the battery to Row through the uaper winding 148 of the relay RT to'hring a outthe energization' of the'relay RT. The role RT energizing opensits normally closed contact 130 to interrupt-the locking circuit of the relay BC. The said relay RC restoring disconnectstlie' ringing interrupter 1' to prevent further upplication of ringing current to-the culled conductor 108,

:A' an" audible :m a is in a. demerii kind" the through' tlli hate! ntalct l2 8, coh Ii 12?, noradrenatactismound-13131 o id ewte 182*1111'6 133,- to drdimd at nt ruute'omm 124: Tliofwo su ervieori'rf lqmgand CB Being lig if'chinniiciite'toi: operutor tliatthe'cull' ing'sulii icriber hath replhbed hie receiver.

The circuit is designed for five=piirty rin' lng; and should the ring'ing generator G'lseused, the actuation-*of'the lreywhich controls therin'ging curr'entfor the said 'genorator G causes a'zfy'one of the key plhngers which is' in indicating 1position to be released, and"this actuationo' the key, con'tiollln currentf'fmm'generetor Gfi-actuates the ori sprin 138 and 139 to causethe relhys IC' and B to be energized; as previously described. The pntlr'for the ringing current to the called suhscribers substation may be traced from the ungrounded pole of the generator G, over conductor 160, throu h the lower winding 162 of the relay R conducto'r 163, to the closed ringing plunger conta ts 137, 136, 136 and 134, conductor 164, through the upper winding 148 of the relay RT, conductor 149, alternate contact 118, tip contacts of the plug CP' and jack J, through thccondenser and call'bell of the 'battery 'clreuit; said receiver-"being ami nutomntimmeanmioedisconnecting said said" link circuits when said link circuit 5 toretelephone from said subscribers mnnecte'd to saideubscribefis telephone line, lmemnd 'for'removing said operators -remea,ns"for-operativel associating seid o eroeive'p fromacross said-Wheatstone bridge" ators'trnnsmitter 'with said ieeeiver w hen circuit. saidg telephone line is connected to 5215 d link 'tel'ephone'systom rncmmng a snucircuit and resistance devices and circuit scribelstelephonedinean operatorstele-" connections for-the same to lacesaidre phone for connection tliereto, a pair of in- *ceiver' hi e-balanced bridge circuit so-that" duction coil vvindinis, and a resistance for the'cirenit isan nnti-side-tone circuit when raid-l0 telep jo'na're transmitter and the receiver:-'is-'bein used-for receiving pnr a NOQIVQIH fo'i' naid' operators telephone, circuit-oonnectimis for connecting satid induc 8. A telephone system tion' obilwindin 'Asai'clresistance, and eeiu F'scribers telephone lines, subscribers lineg ;a'Wlieatstone bridge-cir-= oiated with said' telepho onit lmlfl townmect-ndid -o "were receiver tors te'lephone set inclu ncrofis'ai'd Wh'entstone bet ge circuit to me e-receiver? and including snn= link circuits assonc lines, an operading an operatorsan operatofe transmitter. a-

ventfsifi tonhlifmrn beifig ftransmitted 'frdm" battefi, a retardation coil and'acondeneer said g iperator strnitsniitter to enidoperatofinorrn 3 operatively connected with said reoeiwer, finii al wmttioifil' i sponsive' tkv tranhmitterggsaid receiver being normally-iii- -.thevfdieeonnection' ofi sgiid o retoflsj tele ophrntirely associated with said transmitter, phone'lfiroin saiii slib'eerihqrn lihe to ren rilen-mulbmatic mennefior connecti said -opernsaid' o 'eralwi s neceivei i cnpawle efrecen "torfi telephone: to' one of sei subscribers in fisi octane. frm s id epiraters trensq linesemiarid 'line-"ieconnected to one'of mi rf. "eaid (link c rcuits, means for opermtively cs sum-weir noney tem ncmqmg ag-sun- -eoeiating-esiidwreceiver witlrsaid transmitter scrib'en dphong i; nl plfirflifiy dfqtjpe when snoh connectiontakes plnrceyre'sistcncr erators link circuits, an operntors telephb'ng clevlce'e aud circnit connections to pleces'aid associatedZwitli sajtljlinli' oiroifitei -nn operadevices in- 'e Wheatstone bridge circuit- -nnd' m lgigmpsidb' 11am'e-ifele'pliom'z}cii'iiitr incliidi connect said receiver 'across 'saicl bridge to r decnetlise the-sidmtone, lated to th'e transd itter of snid operator s 91 5A telephone s Stem including a" unri n -im gri agflqd i e' g yi gi seribfis telephone ine, an operator tele-t ofisatjd-Q 'flator oord il'cifif-foreflective "phone adapted to be connected thereto,-re lyi 488866185118 said 'operators 1 trensmitter 'sis'tance devices, circuit connections for contnd i'ecei'ver-w'ylien' one ofithe eorwcircuitn*inecting said devices in n. is connected to the' snfidrilieflsweleplionecirouiq a. receiver for 's'aid operato1"s-tele-- liner; -1gne-adapted to be "connected across said es m relepncne steminclunm'g-a- -suneets tone-bridgencircuit, m'emn for conscribefi telephone ine; [an-' 0 eret'qrs" link -=necting'saidoperator's telephone to said sub- 'circuitifor -oonnection thei 'ev vl thg n-n-opem- 'scribers line, and for connect-in"- said op- 106 torstolephonmssobinted with s'aid }'bpe1'a'- erabors receiver across siiid fifhent'etonc tors link circnit, a transinitter=and"n rebridgecircnit, and means for disconnecting ceiver fonenid operators telephone isa i'ci 'said' 'opemtors telephone from said sub transmitter being-normally connected in'a 'sorih'ers line and for rlisconecting said 0 nbrniallt 'e1'at ')1"s receiver from across siurl Wheat 110 'eaid tran's wet ne brid e circuit;

l0.- A: to e hone system; including a line, on operators receiver; impedance devices,

inopelrati-ve'ly associated with rtiitter,-and meansnssociated with said-cord circuit for operatively associating said operatorfe'trensmitterwith-said operntors re circuit connections connecting said imperlcei-rer} when sai'gfoperator'si telephone i's nnoe devices in n W heatstone bridge circuit, 116 connected-to 'said subscribers telephone line, means for connecting said operntors reso an to laee said receiver in a balanced ceiver ac-rms said Whentstonehrid e circuit. bridg'ec'irenit when the receiver is used for "with said subscribers telephone inc, and receiving purposes. means for disconnecting said operators re- 7. A telephone s ste ceiver from said subscrihers line and from 120 scribers' tele hone 'ne, :1 pluralityof link across saidllheutstone bridge circuit. circuits associated-with saidtele hone line; 11. A system of the character described an operntors telephone associate with saith including a plurality; of connecting circuits, vlinlr-circuits,snid operators telephonebeiflgenopcrators telephone including a. receiver provided with-n transmitter normally inand 'a'trensmitter, saicl tronsrnittcr being 126 operntively associated with theoperatofle normally supplied with operating current, receiver, a retardation COll and a Battery said receiver being normally inoperntively normally connected in circuit with fseid associated with said transmitter, a relay for transmitter, nutomaticmeenn-for connecting each of'said connecting circuits, and means -said operatofls telephone with anyone of controlledhy any one of said relays for 130 121 including a sub- 'lVheatstone bridge 100 telephone adapted, to be jconnec vniary windingfdf the deduction-10ml; hp,

effectively associating said, operntor slre-ficciver with said operatorsu'ansmitter.

12. A- system of the character-described including a connectingciicuiwan'o rato'rs -LWi' i circuit, :1- receiver for saidgg) ereiofistelephone}, normell} inoperatijve associated. with the transmitter-of said perator,s tale phone, an induction coil, the said trimsmifiter i; being normalloperativelyiconneeted with'i the primary winding of the induction coiL-to cfiect changes therein;-w,hen-.the. .said transmitter is actuated, sndsnensassocintedawitlt-inem ter e g said connecting cireuitqfoe cenneeting said- :operators telephone with seid. ;coI rnectin circuitnn for. 0 ratixely; associatms sai receiver withsni tlfldlSIIlltlJEI-q c-L ,Systfl -flfn the character including ai 41110 I pl ra ty o connecting-armistice en operators; nlephnne nnotatedc nn ct g .cirsuitsemreoem smdi i-litl'wi-uc sficmhngfisalfl,

mitten for saicl-iepem oristelephout dn: i-M1 5 t e]? phone to, saidlinlr'circuit means for automatically disconnectingseid operators telephone from said link circuitandfor preventing' side vtone .fi'onnebeing transmitted fromsaid transmitter to said receiver, and means for pr'eventingthe operetors receiver from receivingside tone when the o erators telephone is connected to these-id ink circuit. 17. A telephone system.-inc.ludin,g; a-n;=operntors, telephone provided with e. transmitternndla receiver, an induction coil, said i normally; connected in circuit with in battery end, a primary wind- ;ingmf the induction coi'l saidl-recciver beinginonrn v connectedjto a secondary winding iofithe: induction coilat one point; but being seet se y a s ated i 9 hatth teeeir s. no ally incited M i s-c muit,-me ns zvf r circuit-with said -operaone end, rendering said operaitorggepervencifeetive, said operators rem+,,-.ceiver being connected in a balanced circuit esta -re u e heme-tones irom eid-op wtrflIDLtQPlFh8H the same is usedior transand means in anyone of seid linkmireuim -.for automatically connecting sdidioperatqrfsg with the .induction,

were, telep qn pl' vl fi n h w tr n mitter-nnd'g, teceiyen-andnduction coil, said,

trensm itten. being; 1 normally; (connected in l,

z-circuitwith e buttery and e-primary wind ing ofthcinduction coil, saidreceivenbeing mormclly eonnected to n secoudery winding including telephonelines, e couiiectin coir-in ot the induction coiinten point-bub being cuit for, useuu in erconnecting. sa,id an operators telephone \fb .=J Ql 1Qt10n lSo-.. said connecting. ClIClH-tgzlw receivermndea transmitter for said operatonsg, telephone,-- means for connectin said .opei attirs tel'ephone to said connec mg circuit, and meansfor disconnecting said operetorstelephone; from said connecting circuit'and ion-operas; tively disassociating said receiver-from said transmitter while maintaining-said transmitter in a closed battery circuit. P.

15. A system of the character described including a subscribers telephoneline, a link circuit for extending connection from] said telephone line, an operators telephone including a receiver and a transmitter, means for connecting said operator's tele-' phone to said link circuit, and automatic means individual to said link circuit for dismonnecting said operctors telephone from said link circuit and for operatively disassecinting said receiver from said trunsmitter, said transmitter however remaining in a closed battery circuit.

16. A system of the character described including a subscribers telephone line, a. link circuit for extending connection from said telephone line, an operators telephone including a receiver and a. transmitter, means for connecting said operators tele- -ino ,ratively esociated with the induction coi so that the receiver is normally inefl'ec- .-tive-;for,- receiying, e 1111]; circuit, .meens for ussociatingfvsaid link circuit with said operatorstelephone end rendering said operators receiver effective, said operstors receiver bein comiected in a. bnlnncedcircuit to reduce t e side tones; from said operators transmitter when the same is used for transmission untilthev become substantially-1m noticeable, said receiver ,also being connected -for., eceiving purposes from. said link circult.

19. A system of the charecter described ;.including an o'pemtors telephone and a link circuit, said operator s telephone including a. transmitter normally connected in a bet tel'y circuit, a. receiver normally ineffectively associated with the transmitter, autxnnntivv means for connecting the operators tele phone to the link circuit and for renderiing said receiver efi'ective, circuit connections rendered effective when the operators telephone is connected to the link circuit to con nect means to place the operators receiver in a balanced circuit so that when speech is transmitted b said transmitter the same is reduced in the operators receiver but is transmitted to the link circuit.

7 20. A system of the character described including an operators telephone and a link circuit, said operators telephone including a transmitter normally connected in a battery circuit, a receiver normally ineifectively associated with the transmitter, automatic means for connecting the operators telephone to the link circuit and for rendering said receiver efl'ective, circuit connections rendered effective when the operators telephone is connected to the link cn'cuit to place said receiver in a balanced circuit so that when speech is transmitted by said transmitter the same is substantially inaudible in the operators receiver but is transmitted to the link circuit, said connections being such that when speech is transmitted through said link to said operators telephone the receiver is effective to receive such speech.

21. An operators telephone circuit including a transmitter, a receiver connected in a. balanced bridge circuit so that when the operators telephone is connected for use the current flow through the operators receiver is reduced when the operators transmitter is actuated, and means for rendering ineffective the operators receiver when the operators telephone is not connected for use.

A system of the character described including an operators telephone provided with a normally charged transmitter a circuit for connection to said operator's tele phone an operators receiver for said operators circuit connected in a balanced bridge circuit so that the current How is reduced through the receiver when the operators transmitter is actuated, until it becomes substantiall unnoticeable, and means for eil'ectively dlsassociating the operators receiver from the operators transmitter when the operators telephone is not connected with said first circuit.

Signed by me at Chicago, in the county of Cook and State of Illinois, this 21st day of May, 1918.

CHARLES SPARKS. 

